18650 lithium battery and soft pack battery who is more suitable for electric cars

18650 is the originator of lithium-ion battery--a standard lithium-ion battery model that Japan SONY Company set in order to save cost. Among them, 18 means diameter 18mm, 65 means length is 65mm, 0 means cylindrical battery.

The common 18650 battery is divided into a lithium ion battery and a lithium iron phosphate battery. The lithium-ion battery voltage is 3.7V, the charge cut-off voltage is 4.2v, the lithium iron phosphate battery has a nominal voltage of 3.2V, the charge cut-off voltage is 3.6v, the capacity is usually 1200mAh-3350mAh, and the common capacity is 2200mAh-2600mAh. .

The 18650 battery life theory is cyclic charging 1000 times. Due to the large capacity per unit density, most of them are used in laptop batteries. In addition, the stability of the 18650 is very good at work. It is widely used in various electronic fields: it is often used in high-end glare flashlights. Power supply, wireless data transmitter, electric heating clothing, shoes, portable instrumentation, portable lighting equipment, portable printers, industrial equipment, medical equipment, etc.

1, the capacity of large 18650 lithium battery capacity is generally between 1200mah ~ 3600mah, and the general battery capacity is only about 800mah, if combined into a 18650 lithium battery pack, then 18650 lithium battery pack can easily break through 5000mah.

2, long life 18650 lithium battery has a long service life, the cycle life can reach more than 500 times in normal use, more than twice the average battery.

3, high security 18650 lithium battery safety performance, no explosion, no burning; non-toxic, non-polluting, after RoHS trademark certification; all kinds of safety performance in one go, the number of cycles is greater than 500 times; high temperature performance, 65 degrees The discharge efficiency is up to 100%. In order to prevent battery short circuit, the positive and negative poles of the 18650 lithium battery are separated. So the possibility of its short circuit has been reduced to the extreme. A protective plate can be added to prevent the battery from overcharging and over-discharging, which also extends the battery life.

4, the voltage of 18650 lithium battery voltage is generally 3.6V, 3.8V and 4.2V, much higher than the 1.2V voltage of nickel-cadmium and nickel-hydrogen batteries.

5, no memory effect, do not have to empty the remaining power before charging, easy to use.

6. The internal resistance is small: the internal resistance of the polymer battery is smaller than that of the general liquid battery. The internal resistance of the domestic polymer battery can even be less than 35mΩ, which greatly reduces the self-consumption of the battery and prolongs the standby of the mobile phone. Time can fully reach the level of international standards. This polymer lithium battery that supports large discharge currents is an ideal choice for remote control models and is the most promising alternative to nickel-metal hydride batteries.

7. It can be combined into 18650 lithium battery packs in series or in parallel.

8, the use of a wide range of notebook computers, walkie-talkies, portable DVD, instrumentation, audio equipment, aircraft models, toys, cameras, digital cameras and other electronic equipment.

The biggest disadvantage of the 18650 lithium battery is that his volume has been fixed. It is not well positioned when installed in some notebooks or some products. Of course, this shortcoming can also be said to be an advantage. This is a lithium battery compared to other polymer lithium batteries. This is a disadvantage in terms of customizable and transformable size. It is an advantage over some products with specified battery specifications.

The 18650 lithium battery is prone to short circuit or explosion, which is also relative to the polymer lithium battery. If it is relatively normal, this disadvantage is not so obvious.

18650 lithium battery production needs to have a protection circuit to prevent the battery from being overcharged and causing discharge. Of course, this is a must for lithium batteries, which is also a disadvantage of lithium batteries, because the materials used in lithium batteries are basically lithium cobalt oxide materials, and lithium batteries of lithium cobalt oxide materials can not discharge at high current, safety Poor.

The production conditions of the 18650 lithium battery are high. Compared with the general battery production, the 18650 lithium battery requires high production conditions, which undoubtedly increases the production cost.

The soft-pack lithium battery is simply a liquid lithium-ion battery with a polymer shell. The structure is packaged in aluminum plastic film, and in the case of a safety hazard, the soft pack battery will only burst at most.

1. Good safety performance

Soft pack batteries, unlike steel shell aluminum shell batteries, can explode.

2. Light weight

The weight of the soft pack battery is 40% lighter than the equivalent capacity of the steel shell lithium battery, which is 20% lighter than the aluminum shell battery.

3. Large capacity

The soft pack battery has a capacity of 10 to 15% higher than that of the steel shell of the same size, and is 5 to 10% higher than that of the aluminum shell battery.

4. Small internal resistance

The internal resistance of the soft pack battery is smaller than that of the lithium battery. At present, the internal resistance of the domestic soft pack battery core can be as low as 35 mΩ, which greatly reduces the self-consumption of the battery.

5. Flexible design

The shape of the soft pack battery can be customized according to the customer's needs, and a new battery model can be developed.

The existing soft pack battery core models are few and cannot meet the market demand;

Developing new models is costly.

The same is the world-renowned electric car brand, what makes them different in the choice of power battery? In the field of automotive power battery applications, where are the advantages and disadvantages of the 18650 lithium battery and the soft battery?

As two mainstream power batteries on the market, 18650 batteries and lithium polymer soft pack batteries are distinguished by the package material of the casing. The 18650 battery is generally a steel casing package (18 indicates a diameter of 18 mm, 65 indicates a length of 65 mm, and 0 indicates a cylindrical battery), and the structure of the inner electrode sheet and the diaphragm is a wound type. The lithium polymer soft pack battery is made of aluminum plastic film, and the inner electrode sheet and the diaphragm are stacked (stacked one by one).

Although the shape and internal structure are different, the principles of the two batteries are basically the same. Both batteries have a positive electrode, a negative electrode and an electrolyte. The positive electrode material is generally lithium cobaltate, lithium nickel cobalt manganese oxide (ternary material), lithium iron phosphate or lithium manganate, and the negative electrode material is generally graphite, and the electrolyte is Lithium hexafluorophosphate solution.

The main difference between the two is that the electrolyte is different in one of the internal materials of the battery: the electrolyte inside the lithium polymer soft pack battery is a polymer, generally a gel or a solid, and the electrolyte inside the 18650 battery is generally liquid.

18650 lithium battery and lithium polymer soft pack battery have their own advantages and disadvantages. At present, 18650 battery production has a high degree of automation, battery consistency and safety have reached a high level, and the battery itself is small in size and light in weight, which makes it unique in the modularization and standardization of system development. Many people believe that the use of 18650 battery as the source of power for new energy electric vehicles is the best choice at this stage.

However, the 18650 battery also has the disadvantage of being unavoidable, that is, the monomer capacity is low (generally around 2~4Ah). This makes the 18650 battery require a large number of batteries in the application, and the battery management system that maintains cell consistency and battery cooling is more complicated.

Compared with the 18650 battery, the lithium polymer soft pack battery has a high capacity, and has the advantages of being thinner, arbitrarily aread, and arbitrarily shaped (it is possible to produce ultra-thin batteries of 0.33 mm, 0.50 mm, etc.) The main disadvantages are poor consistency and poor mechanical strength. Based on the characteristics of lithium polymer soft pack batteries, lithium polymer soft pack batteries are increasingly being used in mobile phones, notebook computers, mobile power supplies and other fields. However, due to the poor conductivity of the colloidal (or solid) electrolyte and the large internal resistance, lithium polymer soft pack batteries are rarely used in electric vehicles.

Since lithium polymer soft pack batteries are rarely used in electric vehicles, what type of batteries are Nissan Leaf's cascading soft pack batteries?

In fact, although lithium polymer soft pack batteries are generally referred to as soft pack batteries, soft pack batteries are not all lithium polymer batteries because they can also use liquid electrolyte. Nissan Leaf's battery is a soft pack battery with liquid electrolyte.

Whether it is a lithium polymer soft pack battery or a soft pack battery whose internal material is a liquid electrolyte, the soft pack battery is generally packaged in an aluminum plastic film. The thickness of the aluminum plastic film is thin and the mechanical strength is poor. In the extreme case of collision of the automobile, the aluminum plastic film is prone to breakage and cause accidents, which is the main defect of the soft pack battery used in the new energy vehicle.